Field of the Invention
This invention is concerned with the removal of hydrogen sulfide from a mixture of gases.
In many industrial processes and in the oil production industry, concern over pollution has compelled the more complete removal of harmful or offensive gases from effluent gas streams before release into the atmosphere. Also, many chemical processes demand streams of gases of specific composition.
The problem is to separate gases from each other efficiently and economically.
A gas which is of particular concern as a pollutant is hydrogen sulfide. Hydrogen sulfide and other sulfur compounds are both offensive and harmful. Hydrogen sulfide, for example, can cause corrosion problems and is also toxic in concentrated amounts. Even in considerably less than toxid concentrations, hydrogen sulfide has an offensive odor.
The removal of hdyrogen sulfide is complicated by the fact that it often occurs as a component in a mixture of gases. One frequently occurring mixture of gases is hydrogen sulfide and carbon dioxide. Carbon dioxide is usually tolerated and not considered as a pollutant. Thus, it may be released into the atmosphere. There are many processes which will remove both hydrogen sulfide and carbon dioxide from gas streams and a few which may be made to preferentially remove hydrogen sulfide. Some of these processes use in combination or alone, monoethanolamine and diethanolamine. Others use propylene carbonate, a combination of an alkali metal carbonate and an alkali metal arsenate, and others use a mixture of tetrahydrothiophene-1,1-dioxide and alkanolamines. It is also known in the art to use an aqueous basic solution to remove both carbon dioxide and hydrogen sulfide since both gases increase in solubility in aqueous solutions as the pH of the solution rises.
These prior art processes have disadvantages such as requiring addition of fresh reagents as the active ingredients are used up in the process or regeneration of these active ingredients. In many of these processes, carbon dioxide will neutralize or inactivate the active ingredients and result in inefficient hydrogen sulfide removal and/or compel frequent regeneration of reagents. Also, because of carbon dioxide absorption problem, constant surveillance and manipulation of the absorption system may be required. The present invention overcomes these problems by providing inexpensive, self-regulating aqueous solutions which effectively absorb hydrogen sulfide and allow most of the carbon dioxide to remain in the aqueous phase.